1. Field of the Invention
The present invention relates to a fundus camera which performs alignment while observing an operation distance index.
2. Description of the Related Art
In a conventional fundus camera, when an operator photographs a fundus image, a light flux is projected from the periphery of a pupil of a subject's eye, and a fundus reflection light flux is taken out from a center of the pupil as a photographing light, so that a photographing light flux has a small diameter. Thus, if the light flux deviates even a little, the pupil shades the light flux, so that a flare easily enters in an imaging plane. For performing correct positioning, it is necessary to stabilize a fixation, match alight axis of the subject's eye and an optical axis of a fundus camera optical system, and adjust alignment to a proper position.
Japanese Patent Application Laid-Open No. 62-34530 discusses a fundus camera which projects an alignment index on a cornea of a subject's eye, and determines whether the alignment index is on a proper alignment position in a state that an alignment image which is a reflection image of the projected alignment index in focus. Japanese Patent Application Laid-Open No. 7-31590 discusses a fundus camera which projects an alignment index on a cornea of a subject's eye, and determines whether the alignment index is on a proper alignment position based on separation or matching of an alignment image.
Japanese Patent Application Laid-Open No. 7-31590 and Japanese Patent Application Laid-Open No. 2000-287934 discuss a technique for moving a light guide for projecting an operation distance index. In this technique, the light guide is moved so that a proper operation distance when a fundus peripheral part is photographed is becomes longer than the proper operation distance when a fundus center part is photographed. However, this operation is not for detecting the operation distance.
In the above described conventional fundus cameras, since a light emitting diode (LED) light source having one kind of single wavelength is used as a light source for an alignment index, it can be determined whether the alignment index is in a proper alignment position or not. However, it cannot be determined whether the fundus camera is in a near position with respect to a subject's eye or in a far position in the proper alignment position.
Therefore, for operating the fundus camera to a proper alignment position, an operator moves the fundus camera once toward either direction of closing to or separating from the subject's eye, and determines a direction for closing to the proper alignment position based on whether a defocusing degree and a separation degree increase or not. There is no problem when an operator can move the fundus camera to aright direction for alignment by chance. However, when the operator moves the fundus camera toward an inverse direction, the operation for moving the camera is wasteful.